class, qconfig_mapping, example_inputs, prepare_custom_config=None, backend_config=None)[source]

Prepare a model for quantization aware training

  • model (*) – torch.nn.Module model

  • qconfig_mapping (*) – see prepare_fx()

  • example_inputs (*) – see prepare_fx()

  • prepare_custom_config (*) – see prepare_fx()

  • backend_config (*) – see prepare_fx()


A GraphModule with fake quant modules (configured by qconfig_mapping and backend_config), ready for quantization aware training

Return type



import torch
from import get_default_qat_qconfig_mapping
from import prepare_qat_fx

class Submodule(torch.nn.Module):
    def __init__(self):
        self.linear = torch.nn.Linear(5, 5)
    def forward(self, x):
        x = self.linear(x)
        return x

class M(torch.nn.Module):
    def __init__(self):
        self.linear = torch.nn.Linear(5, 5)
        self.sub = Submodule()

    def forward(self, x):
        x = self.linear(x)
        x = self.sub(x) + x
        return x

# initialize a floating point model
float_model = M().train()
# (optional, but preferred) load the weights from pretrained model
# float_model.load_weights(...)

# define the training loop for quantization aware training
def train_loop(model, train_data):
    for image, target in data_loader:

# qconfig is the configuration for how we insert observers for a particular
# operator
# qconfig = get_default_qconfig("fbgemm")
# Example of customizing qconfig:
# qconfig =
#    activation=FakeQuantize.with_args(observer=MinMaxObserver.with_args(dtype=torch.qint8)),
#    weight=FakeQuantize.with_args(observer=MinMaxObserver.with_args(dtype=torch.qint8)))
# `activation` and `weight` are constructors of observer module

# qconfig_mapping is a collection of quantization configurations, user can
# set the qconfig for each operator (torch op calls, functional calls, module calls)
# in the model through qconfig_mapping
# the following call will get the qconfig_mapping that works best for models
# that target "fbgemm" backend
qconfig_mapping = get_default_qat_qconfig("fbgemm")

# We can customize qconfig_mapping in different ways, please take a look at
# the docstring for :func:`` for different ways
# to configure this

# example_inputs is a tuple of inputs, that is used to infer the type of the
# outputs in the model
# currently it's not used, but please make sure model(*example_inputs) runs
example_inputs = (torch.randn(1, 3, 224, 224),)

# TODO: add backend_config after we split the backend_config for fbgemm and qnnpack
# e.g. backend_config = get_default_backend_config("fbgemm")
# `prepare_qat_fx` inserts observers in the model based on qconfig_mapping and
# backend_config, if the configuration for an operator in qconfig_mapping
# is supported in the backend_config (meaning it's supported by the target
# hardware), we'll insert fake_quantize modules according to the qconfig_mapping
# otherwise the configuration in qconfig_mapping will be ignored
# see :func:`` for a detailed explanation of
# how qconfig_mapping interacts with backend_config
prepared_model = prepare_qat_fx(float_model, qconfig_mapping, example_inputs)
# Run training
train_loop(prepared_model, train_loop)


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